1. Field of the Invention
The present invention relates to a method and to an apparatus for applying horizontal markings to roads or other traffic areas, using water-thinnable emulsion paints.
2. Description of the Related Art
Horizontal markings, especially limiting, guiding and warning lines, are generally applied using a marking vehicle which is equipped with paint spray guns for spraying the marking paint and, optionally, with bead scatterers for applying reflective beads, as described, for example, in EP-B-0 280 102.
Marking paints containing solvents are known generally, but their use is being increasingly criticized for reasons of environmental protection. Also known are water-thinnable emulsion paints, which are more environmentally friendly.
A disadvantage common to both types of marking paints, however, is a fairly long drying time, of in general from 10 to 30 minutes. At a drying time of, for example 20 minutes and a marking rate of 6 km/h, therefore, it is necessary to close off a stretch of 2 km at a time behind the operations site with the aid of a blocking gang, resulting in considerable hindrances and hold-ups for traffic. Furthermore, marking work has to be interrupted in inclement weather and when rain threatens, so as to avoid the possible running of paint which has not yet become water resistant.
EP-A-0 200 249 describes a process in which an aqueous emulsion paint is caused to dry within 15 minutes--in specific cases in 6 minutes--after application, by the addition of a water-soluble salt, for example sodium chloride, calcium chloride or the like. The quantity of salt is from approximately 15 to 25 g per m.sup.2 of painted surface.
EP-A-0 409 459 describes acid-coagulable emulsion paints which contain, in particular, an anionic stabilized polymer emulsion and a polyfunctional amino polymer and which are stabilized in the alkaline range by a volatile base. After application the base evaporates, so that the pH falls and, as it passes the pH of coagulation, the paint solidifies. The drying time is from 10 to 20 minutes or more, depending on the temperature and the degree of atmospheric humidity, which are factors which affect the evaporation of the base.